Over the years, supermarkets have established rather strict rules governing the dimensions of display units in order to ensure that they will not interfere with, or even endanger, people moving along the lanes delimited by the shelves, or that some of these units will not impair the visibility of other display units and, of course, of the products. Thus, the size of display units mounted in a direction perpendicular to the shelves is limited to a size of up to about 13.times.20 cm, while units mounted parallel to the shelves, and thus not projecting into the lanes, may be of a size of up to about 30.times.30 cm. None of these display units, however, may depend on external power sources, which would imply stringing of wiring along the shelves and the provision of outlets at fixed points, restricting flexibility.
Today the display units used are in the form of plastic frames attached to the shelves and carrying cards with what is intended to be a sales-promoting message. Over the years, however, the attention-commanding power of these passive displays has progressively waned and something more compelling is required to effectively attract the attention of today's sophisticated public.